Illustrated herein, in various embodiments, are methods for preparing encapsulated bichromal balls and/or other rotatable elements, such as bichromal beads, spheres, etc., and the encapsulated products produced thereby. These methods and encapsulated products find particular application in conjunction with display devices and substrates using bichromal balls, and will be described with particular reference thereto. However, it is to be appreciated that the present exemplary embodiments are also amenable to other like applications.
Bichromal rotatable elements, such as bichromal balls or beads (or Gyricon balls or beads as sometimes referred to in the art), are tiny spheres, such as micron-sized wax beads, which have an optical and an electrical anisotropy. These characteristics generally result from each hemisphere surface or side having a different color, such as black on one side and white on the other, and electrical charge, i.e., positive or negative. Depending on the electrical field produced, the orientation of these beads will change, showing a different color (such as black or white) and collectively create a visual image. A wide assortment of different color combinations (black/white, blue/white, red/white, blue/yellow, etc.) are possible making the products useful for the fabrication of display devices, such as electrophoretic or photochromic displays.
In this regard, the spherical particles are generally embedded in a solid substrate with a slight space between each ball and the substrate being filled with a liquid so that the balls are free to rotate in a changing electrical field, but can not migrate from one location to another so as to disrupt the arrangement of rotatable elements. If one hemisphere of the balls is one color (i.e., black), and the other is a different color (i.e., white), each pixel can be turned on and off by the electrical field applied to that location. As a result, each pixel can be individually addressed, and a full page image can thus be generated.
For example, reusable signage or displays can be produced by incorporating the tiny bichromal beads in a substrate such as sandwiched between thin sheets of a flexible elastomer and suspended in an emulsion. The beads reside in their own cavities within the flexible sheets of material. Alternatively, the tiny bichromal beads or balls can be encapsulated in a suspending or electrophoretic fluid. The encapsulated bichromal beads or balls can be affixed to a support to form a display device. Under the influence of a voltage applied to the surface, the beads will rotate to present one side or the other to the viewer to create an image. The image stays in place until a new voltage pattern is applied using software, which erases the previous image and generates a new one. This results in a reusable signage or display that is electronically writable and erasable. This is sometimes referred to as “electric paper” or “e-paper”.
Numerous patents describe bichromal balls, their manufacture, incorporation in display systems or substrates, and related uses and applications. Exemplary patents include, but are not limited to: U.S. Pat. Nos. 5,262,098; 5,344,594; 5,604,027 reissued as U.S. Pat. Nos. Re 37,085; 5,708,525; 5,717,514; 5,739,801; 5,754,332; 5,815,306; 5,900,192; 5,976,428; 6,054,071; 5,989,629; 6,067,185; 6,235,395; 6,419,982; 6,488,870; 6,445,490; 6,549,327; and 6,703,074; all of which are hereby incorporated by reference.
Hydrocarbon oils such as ISOPAR M have been used as encapsulant liquids or fluids for bichromal balls in “electric paper” available from Gyricon, LLC. However, the long-term stability of bichromal balls in ISOPAR oils has been a concern. As a result, polysiloxane oils have been used as encapsulant liquids or fluids in place of ISOPAR oils in some current electric paper displays. However, polysiloxane oils are difficult to encapsulate together with the waxy bichromal beads to form uniform encapsulated bichromal balls. The poor compatibility of the waxy beads and low viscosity polysiloxane oil often fails to produce the desired encapsulated balls. Hence, a need remains for an encapsulant liquid or suspending fluid with improved properties and long-term stability.